The present invention relates to a method of forming an insulating film and, more particularly, to a method of forming a silicon oxide film containing fluorine.
As a conventional method of forming a silicon oxide film of this type, a chemical vapor-phase deposition method is popularly used. For example, the following method is used. That is, tetraethylorthosilicate (chemical formula: Si(OC.sub.2 H.sub.5).sub.4) serving as a source gas is evaporated by bubbling and then mixed with ozone in a reaction chamber so as to form a silicon oxide film at a substrate temperature of 300.degree. C. to 400.degree. C. and an atmospheric pressure. In addition, a method of doping phosphorus and boron by using trimethylphosphate (chemical formula: PO(OCH.sub.3).sub.3) and trimethylborate (chemical formula: B(OCH.sub.3).sub.3) as doping gases is used ("Ozone/Organic-Source APCVD for Conformal Doped Oxide", Journal of Electronic Materials, Vol. 19, No. 1, 1990).
This conventional method of forming a silicon oxide film has the following problems. That is, since a temperature for forming a film is high, i.e., 300.degree. C. to 400.degree. C., a silicon oxide film cannot be selectively formed by using an organic film such as a photoresist film as a mask. In addition, when the temperature is decreased, film properties are considerably degraded, and the film cannot be disadvantageously used in practical applications. Furthermore, since a silicon oxide film formed in the conventional method has a strong tensile stress of about 1.times.10.sup.9 dyn/cm.sup.2 as an internal stress, when a film having a thickness of 2 .mu.m or more is formed, cracks easily occur in this film. For this reason, this film is not easily formed on a substrate such as an aluminum wiring layer having an uneven surface.